How can I reduce polycount without using decimate?
There are some but they'll all require some tweaking.  Investigate Decimate further, because there's some angle-limited options in there that are pretty good, and don't destroy the mesh as much, and if you can get it to do it for you then it'll be far less work.

However if you're set on not using Decimate then you may instead have to do it by hand.

Start selecting edge loops you don't need and dissolving them, as well as collapsing verts and edges wherever you think you can get away with it.

If you'd rather start from scratch as it were, you can make a new mesh and shrinkwrap it to your current one using the Shrinkwrap modifier.  Extrude sides, add new vertices, etc.  This way you can put topology exactly where you need it, and exactly how much of it is necessary and no extra.  This process is called Retopology and there's a lot of more detailed information out there available with a bit of searching.